6 



BULLETIN 1010, U. S. DEPARTMENT OF AGRICULTURE. 



centage of earth used. Seven per cent of earth appears to be the 

 most beneficial, but from a practical standpoint 5 or 6 per cent is 

 sufficient, since no reduction in red is obtained with higher propor- 

 tions. There is a limit, of course, to the proportion of earth which 

 may be used in practice. The expense involved would not justify 

 the use of more than 6 per cent. The expense lies not only in the cost 



40 



35 



8 



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 N 5 



Tempera tore 



T/ME 



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% OF earth yeuow 



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o 



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7 



36. a 



30.4 

 230 



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 /OS 



40 

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Z <f 7 



Percent oe Fullers Earth 



/o 



Fig. 1.— Relation between the pioportion of fuller's earth used and the extent of the bleaching effected. 



of the earth, but in the additional loss of oil which is entailed by the use 

 of the greater quantities and the somewhat greater expense of 

 filtering. Fuller's earth generally shows less bleaching efficiency when 

 used in laboratory quantities than when used in large-scale opera- 

 tions. Hence, the use of a maximum of 5 or 6 per cent of earth, as 

 generally practiced in refineries, would seem to be in accordance with 

 the results of these tests. 



